La doped Pt/TiO2 as an efficient catalyst for room temperature oxidation of low concentration HCHO

Chinese Journal of Catalysis 38 (217) 39 47 催化学报 217 年第 38 卷第 1 期 www.cjcatal.org available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/chnjc Article La doped Pt/TiO2 as an efficient catalyst for room temperature oxidation of low concentration HCHO Honggen Peng a,b, *,, Jiawei Ying a,, Jingyan Zhang a, Xianhua Zhang a, Cheng Peng a, Cheng Rao a, Wenming Liu a, Ning Zhang a, Xiang Wang a,# a Institute of Applied Chemistry, College of Chemistry, Nanchang University, Nanchang 3331, Jiangxi, China b School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 224, China A R T I C L E I N F O A B S T R A C T Article history: Received 3 August 216 Accepted 21 September 216 Published 5 January 217 Keywords: Low concentration formaldehyde Room temperature oxidation Rare earth Lanthanum doping Platinum Titania Monolithic catalyst Catalytic oxidation of formaldehyde (HCHO) is the most efficient way to purify indoor air of HCHO pollutant. This work investigated rare earth La doped Pt/TiO2 for low concentration HCHO oxidation at room temperature. La doped Pt/TiO2 had a dramatically promoted catalytic performance for HCHO oxidation. The reasons for the La promotion effect were investigated by N2 adsorption, X ray diffraction, CO chemisorption, X ray photoelectron spectroscopy, transmission electron microscopy (TEM) and high angle annular dark field scanning TEM. The Pt nanoparticle size was reduced to 1.7 nm from 2.2 nm after modification by La, which led to higher Pt dispersion, more exposed active sites and enhanced metal support interaction. Thus a superior activity for indoor low concentration HCHO oxidation was obtained. Moreover, the La doped TiO2 can be wash coated on a cordierite monolith so that very low amounts of Pt (.1 wt%) can be used. The catalyst was evaluated in a simulated indoor HCHO elimination environment and displayed high purifying efficiency and stability. It can be potentially used as a commercial catalyst for indoor HCHO elimination. 216, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved. 1. Introduction Formaldehyde (HCHO) emitted from newly installed building materials, plastic cements and paintings is one of the main air pollutants in the indoor environment, which seriously affects people s health even at concentration lower than a few ppm [1 5]. As one of the most toxic air pollutants, HCHO has a negative influence on genetic material, respiratory tracts and cutaneous covering and also strongly affects the central nervous system [6]. Therefore, in order to improve indoor air quality and reduce public health risk, the abatement of HCHO at room temperature is a problem which should be urgently solved. Over the past decades, many efforts have been made to investigate the removal of HCHO by environmental scientists [1]. Technologies that have been studied for the removal of HCHO are adsorption, photo catalysis, plasma technology, and catalytic oxidation [3,7 11]. Adsorption is a useful method for indoor air HCHO removal. Some absorbents can successfully reduce indoor HCHO concentrations to very low levels [12 14]; * Corresponding author. Tel: +86 158351832; E mail: penghonggen@ncu.edu.cn # Corresponding author. Tel: +86 15979149877; E mail: xwang23@ncu.edu.cn These authors contributed to this work equally. This work was supported by the National Key Research and Development Program (216YFC259), the National Natural Science Foundation of China (215316, 2156716), the Education Department of Jiangxi Province (KJLD145), and the Natural Science Foundation of Jiangxi Province (2142BAB21313 and 2151BBE56). DOI: 1.116/S1872 267(16)62532 9 http://www.sciencedirect.com/science/journal/1872267 Chin. J. Catal., Vol. 38, No. 1, January 217

4 Honggen Peng et al. / Chinese Journal of Catalysis 38 (217) 39 47 however, their effectiveness is limited by adsorption capacity and they produce secondary pollution during regeneration. Photo catalysis has received wide attention over the past decades and has been widely applied in energy production and environmental protection [15 18]. However, the photo catalytic process requires the assistance of light energy, which may not available for the elimination of an indoor air pollutant and its wide application is limited. Catalytic oxidation can selectively decompose the toxic HCHO into harmless CO2 and H2O at ambient temperature [2,19 21]. Thus, the catalytic oxidation is regarded as the most promising method for indoor HCHO removal [1]. There are two major classes of catalysts for the complete oxidation of indoor HCHO: supported or unsupported transition metal oxides [7,8,22,23] and supported noble metal catalysts [3,9 11]. Of the former catalysts, the most efficient metal oxides that have been widely studied are MnOx [7,24], CeO2 [25], Co3O4 [26], and MnCeOx [7]. Although they exhibit high activity at the beginning of the tests, these catalysts are easily deactivated in the presence of H2O (H2O can strongly adsorbed on the surface of the active sites, especially at low temperature), which greatly influences its practical application [7]. For most supported noble metal catalysts, their activity and water tolerance are superior for volatile organic compounds (VOCs) elimination. Supported catalysts, such as Pt/TiO2 [3,27], Pt/Al2O3 [28], Pd/TiO2 [29], and Au/CeO2 [6], have been widely studied and demonstrated high activity for HCHO oxidation. However, due to limited sources and the high price of noble metals, it is currently an important task and hot research topic to design and prepare catalysts with smaller noble metal particle size to reduce their loading. For noble metal based catalysts, it is commonly accepted that their activity is closely related to their particle size [3 33]. When studying the water gas shift reaction on Pd/CeO2 and Pt/CeO2, Gorte and coworkers [3] observed a linear relationship between activity and metal surface area. For methanol synthesis from H2/CO on Pd/CeO2, Shen and coworkers [31] also found that there was a close correlation between activity loss and the growth of the Pd particle size. In our previous studies, we also found that on Pd supported on various supports for CO and CH4 deep oxidation that the activity is closed related to the Pd crystallite size and its metal surface area [34 36]. The same effect was also observed for Ni supported on different supports for CH4 reforming for hydrogen production [37 39]. Therefore, the preparation of ultra small noble metal nanoparticles of Pd, Pt, and Au has recently received a great deal of interest in the field of catalysis due to their size dependent catalytic activity [4 42]. Meanwhile, many previous results have demonstrated that the addition of certain amounts of rare earth oxides can improve the dispersion of supported noble metal catalysts and give much smaller particle size of the active component compared with the non modified ones [43 46]. Therefore, the metal support interaction of noble metal supported catalysts can be enhanced by rare earth modification [44,46 48]. To improve the utilization efficiency of noble metal based catalysts, in the present study, anatase TiO2 was modified by La first and then Pt was supported on it. This catalyst was applied for indoor low concentration HCHO oxidation at room temperature. To the best of our knowledge, there has been no report on the application of rare earth modified Pt/TiO2 for removing the low concentration HCHO at room temperature. The results demonstrated that La doped TiO2 remarkably reduced Pt particle size to below 2 nm. The La modified TiO2 was wash coated on a cordierite monolith and then a very low amount of Pt (.1 wt%) was supported on it. This catalyst was evaluated in a simulated indoor HCHO elimination environment, and it displayed high purifying efficiency and superior stability. 2. Experimental 2.1. Catalyst preparation First, anatase TiO2 was modified by various amounts of La (, 1, 5, and 7 wt% La2O3) using a wet impregnation method. Typically,.411 g La(NO3)3 was dissolved in an appropriate amount of deionized water. Then, 5 g TiO2 (anatase, Aladdin) was added into the La(NO3)3 aqueous solution under constant stirring. After stirring for 2 h, excess water was removed in a rotary evaporator at 8 C under vacuum. The samples were dried at 11 C for 12 h and then calcined at 4 C for 4 h. This catalyst was designed as 3 wt%la TiO2. The other amounts of La modified TiO2 was denoted as x wt%/la TiO2. Second, Pt nanoparticles were supported on La modified TiO2 also by a wet impregnation method similar to that used for La modified TiO2. The amount of Pt was fixed at.5 wt% of the final catalyst, and Pt(NH3)4(NO3)2 was the Pt source. In detail, the.5 wt% Pt/x wt% La TiO2 catalysts were prepared with an aqueous solution of Pt(NH3)4(NO3)2 instead of La(NO3)3 solution. An amount of the prepared x wt%la TiO2 support was measured and added into the Pt(NH3)4(NO3)2 solution. The mixture was constantly stirred overnight at 3 C before removing excess water at 8 C, and dried at 11 C for 12 h and calcined at 4 C in an air atmosphere for 4 h. The sample was reduced by 1% H2/N2 at 4 C for 4 h to obtain Pt supported on La modified TiO2, and designated as Pt/x wt% La TiO2. For commercial application, 3 wt%la TiO2 was wash coated on cordierite monoliths (256 cpsi, 15 cm (length) 15 cm (width) 1.2 cm (height)) first and then a calculated amount of Pt (.1 wt% based on the weight of the monolith) was impregnated onto this modified monolith. Before impregnation, the 3 wt%la TiO2 powder, which was calcined at 4 C for 4 h in air, was wash coated on the cordierite monolith. Prior to wash coating, the monoliths were calcined at 5 C for 2 h (with a ramp rate of 5 C/min) to remove adsorbed water. Then, a solid phase of 5 wt% boehmite (Disperal D) was dissolved in a slurry mixture consisting of liquid H2O was first used for the impregnation of the calcined monoliths in order to enhance the attachment of the 3 wt%la TiO2 powder. The alumina coated monolith was previously calcined at 3 C for 1 h and then 5 C for 1 h (heating rate 2 C/min). Finally, the alumina coated monoliths were immersed into a mixture of 3 wt%la TiO2 slurry (liquid to solid weight ratio = 8/2). The above procedure was repeated several times until the mono

Honggen Peng et al. / Chinese Journal of Catalysis 38 (217) 39 47 41 liths were coated with the desired amount of wash coat. The La TiO2 coated monoliths were further calcined at 5 C for 2 h at a heating rate of 5 C/min. Afterwards, La TiO2 coated monoliths was impregnated by.1 wt% Pt by conventional impregnation, where the amount of Pt was just.1% of the mass weight of the monolithic catalyst. Finally, the Pt/La TiO2 coated monoliths were calcined at 4 C for 4 h, and then further reduced by 1% H2/N2 at 4 C for 4 h. 2.2. Catalyst characterization N2 adsorption desorption isotherms were measured using a Micromeritics ASAP 22 system. The specific surface area (SBET) was estimated using the BET method. The pore size distribution was calculated using the Barrett Joyner Halenda (BJH) method, which calculated the pore size based on the adsorption layer thickness in relation to the pressure and the average radius of the meniscus obtained using the Kelvin method. Each sample was analyzed after degassing in vacuum at 3 C for 4 h. The powder X ray diffraction (XRD) patterns were obtained on a Bruker AXS D8 Focus diffractometer operating at 4 kv and 4 ma with a Cu target and Kα X ray irradiation. Scans were collected over a range of 2θ from 1 to 9 with a step of.3 /s. The calculated experimental error for 2θ measurement of the peaks was ±.1. CO temperature programmed desorption (CO TPD) was measured on an Auto Chem 292 (Micromeritics Co.) to analyze the Pt dispersion of the catalyst. The sample (typically 5 mg) was reduced first in a flow of 1% H2/Ar gas mixture (3 ml/min) at 3 C for 3 min, and then purged by a ultra high purity He flow (3 ml/min) at room temperature for 3 min prior to CO adsorption in a 4% CO/He flow (2 ml/min). Afterwards, the sample was purged again in He flow (3 ml/min) for 3 min to remove physically adsorbed CO. After getting a stable baseline, the temperature was increased to 5 C at a rate of 1 C/min. A CO desorption peak was generally detected for each sample at ~15 C, and the relative CO desorption amount was monitored by a thermal conductivity detector (TCD). X ray photoelectron spectroscopy (XPS) experiments were carried out on an RBD upgraded PHI 5C ESCA system using a single Mg Kα X ray source operating at 25 W and 14 kv. The spectra were obtained at ambient temperature. The binding energies were calibrated using the C 1s peak of graphite at 284.6 ev as reference. The transmission electron microscope (TEM) and high angle dark field scanning transmission electron microscope (HAADF STEM) images were taken on a Tecnai F3 field emission transmission electron microscope equipped with an energy dispersive spectroscopy (EDS) detector to determine the particle size of Pt. Fig. 1. Schematic of the procedure of using a powder catalyst for HCHO oxidation. A: Air; B: Formaldehyde solution; C: Detector; D: Quartz tube; E: Catalyst; F: Detector. reactor (i.d. = 6 mm) in a chamber where the temperature was kept at 25 C, as shown in Fig. 1. Gaseous HCHO was generated by flowing air through the formaldehyde solution container in a water bath kept at 25 C. The feed gas composition was.5 ppm of HCHO, 21% O2 and 5% RH balanced by nitrogen. The weight hourly space velocity (WHSV) was fixed at 6 ml g 1 h 1. The inlet and outlet gases were monitored by INTERSCAN 416 (detection range and limit are 19.99 and.1 ppm, respectively), which is a HCHO detector. To test the performance of the monolithic catalyst, Pt supported cordierite monoliths were placed in an air purifying machine. Then, the machine equipped with monolithic catalyst was located in a 2 m 3 sealed box to evaluate the purifying efficiency of HCHO in a real environment. The initial concentration of HCHO was fixed at about.5 ppm and monitored by a HCHO detector. The procedure for testing the performance of the monolithic catalysts is shown in Fig. 2. 3. Results and discussion 3.1. Catalytic performance of the catalysts Anatase TiO2 was first doped with various amount of La2O3, and then.5 wt% Pt was supported on the La modified TiO2. The catalytic activity of Pt supported on La modified TiO2 powder catalyst for HCHO oxidation is shown in Figs. 3 and 4. The concentration of HCHO was fixed at.5 ppm, which is 2.3. Activity test The activity test for the catalytic oxidation of HCHO over the catalysts (1 mg) was performed in a fixed bed quartz flow Fig. 2. Schematic of the procedure of using a monolithic catalyst for HCHO oxidation. A: Air; B: Formaldehyde solution; C: Sealed chambers; D: Catalytical reaction apparatus; E: Fan; F: Detector.

42 Honggen Peng et al. / Chinese Journal of Catalysis 38 (217) 39 47 1 1 HCHO conversion (%) 8 6 4 Anatase TiO 2.5% Pt/TiO 2.5% Pt/3wt%La-TiO 2 (a) HCHO conversion % 8 6 4.5% Pt-3 wt%la-tio 2 (b) 2 2 1 2 3 4 5 6 7 8 Time on stream (h) 5 1 15 2 25 3 35 4 Time on stream (h) Fig. 3. (a). Catalytic performance of Pt/La TiO2 and Pt/TiO2 and durability test of Pt/3 wt%la TiO2 for HCHO oxidation (b). Reaction conditions: 25 C, initial HCHO concentration.5 ppm, WHSV = 6 ml gcat 1 h 1. about 5 times higher than the allowed upper limit (.8.1 ppm). This concentration is similar to the amount of HCHO emission in newly decorated buildings. There has been no report on HCHO removal using a concentration lower than 1 ppm. It is observed that the catalyst activity was promoted by the doped La as compared with the unmodified one (Fig. 4). The Pt/TiO2 catalyst presented the lowest HCHO conversion at room temperature, just 88%. However, the conversions for the La modified samples were all above 9%. The highest activity of nearly 1% at a GHSV of 6 h 1 at room temperature was obtained when the loading of La2O3 was 3. wt% (Fig. 4). Furthermore, the stability of Pt/3 wt%la TiO2 catalyst in the long term was tested at 25 C. As shown in Fig. 3(b), the sample exhibited excellent long term stability and catalytic activity, and the HCHO conversion was maintained at 1% for 4 h without any decrease. So, we concluded that anatase TiO2 modified by La2O3 had a dramatic promotion effect for HCHO oxidation. 3.2. Characterization of the catalysts The textural properties of the Pt/3 wt%la TiO2 and Pt/TiO2 catalysts were investigated together with pure TiO2 and HCHO conversion (%) 1 95 9 85 8 Pt/1 wt%la-tio 2 Pt/3 wt%la-tio 2 Pt/5 wt%la-tio 2 Pt/7 wt%la-tio 2 Pt/TiO 2 1 2 3 4 5 6 7 8 Time on stream (h) Fig. 4. Catalytic performance of Pt supported on various amount of La modified TiO2. 3 wt%la TiO2 by N2 adsorption desorption measurements. The results are shown in Fig. 5 and the quantitative results listed in Table 1. As can be observed in Fig. 5, all the catalysts displayed type IV isotherm with type H3 hysteresis. The capillary condensation step observed in the isotherms is the characteristic of the presence of mesopores. Moreover, pure TiO2 showed an obviously larger N2 adsorption amount than the others. This was in line with the surface area and pore volume results in Table 1. Among all the supports, pure TiO2 possesses the highest surface area (67 m 2 /g) and pore volume, while the surface area and pore volume showed a slight decrease after modification by La2O3 and doping Pt. The pore size distribution of the catalysts can be seen from the inset image in Fig. 5. All the samples showed two similar groups of pore diameter distribution: one group at 2 nm and the other at 1.6 nm. The former was assigned to the secondary aggregation of the particles, while the latter was assigned to particle micropores. To identify the phase composition of the synthesized catalysts, all the samples were characterized by powder XRD. As the results show in Fig. 6, pure TiO2 showed three diffraction peaks at 2θ = 25.3 (11), 37.8 (4) and 48. (2), which are typical for the anatase TiO2 phase. La species peaks were not observed with modified TiO2, indicating that the La2O3 species were highly dispersed on the TiO2 support. At the same time, the introduction of Pt did not induce the appearances of the peaks of polycrystalline Pt, which can be attributed to the low loading of Pt (.5 wt%) and manifested that Pt nanoparticles with an ultra small size at very high dispersion on the supports were obtained, which was further confirmed by the HRTEM and HAADF STEM images and CO adsorption desorption studies described in the following. To better understand how the La2O3 modification affected Pt dispersion and particle size, CO TPD, HRTEM and HAADF STEM analysis of the catalysts were performed. Pt dispersion was determined by CO chemisorption. The results are listed in Table 1. Without La addition, the Pt dispersion on Pt/TiO2 sample was 51%. La2O3 addition to Pt/TiO2 remarkably increased the Pt dispersion to 66%. Clearly, La addition induced a more dispersed Pt species on Pt/3 wt%la TiO2 catalyst that exposed

Honggen Peng et al. / Chinese Journal of Catalysis 38 (217) 39 47 43 Volume adsorbed (cm 3 /g, STP) Volume adsorbed (cm 3 /g, STP) 16 14 12 1 8 6 4 2 1 8 6 4 2 Pore volume (cm 3 /g) Pore volume (cm 3 /g).25.2.15.1.5. 5 1 15 2 25 3 35 4 Pore diameter (nm)..2.4.6.8 1. Relative pressure (P/P).25.2.15.1.5. 5 1 15 2 25 3 35 4 Pore diameter (nm) (a) (c) Volume adsorbed (cm 3 /g, STP) Volume adsorbed (cm 3 /g, STP).18 1 (b) 8 6 4 2..2.4.6.8 1. Relative pressure (P/P) 1 8 6 4 2 Pore volume (cm 3 /g) Pore volume (cm 3 /g).16.14.12.1.8.6.4.2. 5 1 15 2 25 3 35 4 Pore diameter (nm).25.2.15.1.5. 5 1 15 2 25 3 35 4 Pore diameter (nm) (d)..2.4.6.8 1. Relative pressure (P/P)..2.4.6.8 1. Relative pressure (P/P) Fig. 5. N2 adsorption desorption isotherms and pore size distribution curves of TiO2 and supported Pt catalysts. (a) TiO2; (b) 3 wt%la TiO2; (c) Pt/TiO2; (d) Pt/3 wt%la TiO2. more Pt sites for HCHO oxidation, thus significantly promoting the activity of the catalyst. Pt grain sizes were calculated based on the TEM and HAADF STEM images shown in Figs. 7 and 8. The quantitative results are listed in Table 1. Fig. 7(a) and (b) showed that ultra small Pt particles were well dispersed on the surface of the supports. The calculated Pt particle size was around 2.2 nm. Interestingly, the La2O3 modified samples showed a smaller Pt size of around 1.7 nm as shown in Fig. 7(c) and (d). The results were further confirmed by HAADF STEM, as shown in Fig. 8. The images and results were in accordance with the Pt dispersion determined by CO chemisorption. All the characterization results demonstrated that the addition of La2O3 gave a dramatic improvement of Pt dispersion on TiO2 support, leading to a smaller Pt particle size, more active sites exposed and superior activity for indoor low concentration HCHO oxidation. The turnover frequencies (TOFs) of the La doped and undoped catalysts were.776 and.819 h 1, respectively, which were very similar. This result further verified that the addition of La Anatase TiO 2 Table 1 Physicochemical properties of Pt/TiO2 and Pt/La TiO2 measured by N2 sorption isotherms. Sample SBET a (m 2 /g) Pore volume b (cm 3 /g) Pore size b (nm) Pt dispersion c (%) Pt particle size (nm) Nano TiO2 67.45 25.3 3 wt%la TiO2 65.31 19.7 Pt/TiO2 58.28 18.3 51 2.2 Pt/3 wt%la TiO2 59.27 16.4 66 1.7 a Calculated by BET method. b Determined by BJH method. c Calculated by CO TPD. Intensity (a.u.).5 wt%pt/3 wt%la-tio 2.5 wt%pt-tio 2 3 wt% La-TiO 2 Anatase TiO 2 2 4 6 8 2 ( o ) Fig. 6. Powder XRD patterns of TiO2 and supported Pt catalysts.

44 Honggen Peng et al. / Chinese Journal of Catalysis 38 (217) 39 47 a b.4.35 Pt/TiO2.3 Frequency (%).25.2.15.1.5 1 nm 1 nm c d..5 1. 1.5 2. 2.5 3. 3.5 4. Diameter (nm).4.35 Pt/3 wt%la-tio2.3 Frequency (%).25.2.15.1.5 1 nm 1 nm..5 1. 1.5 2. 2.5 3. Diameter (nm) Fig. 7. TEM images of Pt/TiO2 (a, b) and Pt/3 wt%la TiO2 (c, d) and their Pt particle size. can effectively increase the dispersion of Pt and decrease the particle size of Pt. XPS measurements were carried out to investigate the electronic state of the Pt species to reveal the effect of La2O3 on the Pt/TiO2 catalyst. The results are shown in Fig. 9. Table 2 summarizes the binding energy (BE) values of Pt 4f, Ti 2p and O 1s and the atomic ratio of adsorbed O to lattice O calculated from the XPS results of the modified and unmodified catalysts. It is well known that the Pt 4f7/2 BE of Pt, Pt 2+ and Pt 4+ are 71.1, 72.4 and 74.2 ev [1,11], respectively. For the Pt/3 wt%la a c b d Pt Pt TiO2 catalyst, the peaks of Pt 4f were centered at 71.2 and 74.5 ev, so Pt and Pt 4+ species simultaneously existed on this catalyst (Fig. 9(a)). It can be observed that the peaks of Pt 4f of unmodified Pt/TiO2 were very similar to those of La modified Pt/TiO2. From Fig. 9(b), we can also see that the peak of Ti 2p centered very closely at 457.8 ev. Since the La modified Pt/TiO2 did not affect the electronic state of Pt and Ti, the Pt dispersion and Pt particle size would be the most important factors for the catalytic performance in HCHO oxidation. The O 1s spectra of modified and unmodified Pt/TiO2 are shown in Fig. 9(c). The O 1s spectra exhibited two peaks: a main peak at 529 ev, and a shoulder peak at 531. ev. These results indicated two types of oxygen species existed on the catalysts. The former can be assigned to lattice oxygen (Olat), and the latter to chemisorbed oxygen (Oads). The Oads/Olat ratio was calculated from the peak areas. The results are shown in Table 2. It was found that Oads/Olat was very different between modified and unmodified Pt/TiO2. The Oads/Olat ratio of Pt/La TiO2 was higher than that of Pt/TiO2. Thus the La doped TiO2 can create more oxygen vacancies than the unmodified one, and the metal support interaction would be enhanced due to the generation and activation of more chemisorbed oxygen species. 3.3. Performance of the monolithic catalyst Fig. 8. HAADF STEM images of Pt/TiO2 (a, b) and Pt/3 wt%la TiO2 (c, d). For commercial application, 3 wt%la TiO2 was wash coated on cordierite monoliths and then.1 wt% Pt was loaded on the monoliths by a conventional impregnation method. The monolithic catalyst was tested in a 2 m 3 sealed box to simulate the air environment for HCHO decomposition. The results are shown in Fig. 1. The initial HCHO concentration was.55 ppm,

Honggen Peng et al. / Chinese Journal of Catalysis 38 (217) 39 47 45 (a) 74.5 71.2 (b) 457.8 (c) Intensity (a.u.) 74.8 71.6 (2) (1) Intensity (a.u.) 463.5 463.7 457.9 (2) (1) Intensity (a.u.) (2) (1) 8 78 76 74 72 7 68 Binding energy (ev) 47 468 466 464 462 46 458 456 454 452 Binding energy (ev) 533 532 531 53 529 528 527 Bining energy (ev) Fig. 9. XPS analysis of (1) Pt/TiO2 and (2) Pt/3 wt%la TiO2 catalysts. (a) Pt 4f ; (b) Ti 2p; (c) O 1s. Table 2 XPS results of Pt/TiO2 and Pt/3 wt%la TiO2 catalysts. Sample which is close to the real high concentration in an indoor environment. For the fresh catalysts, the HCHO concentration was decreased to.8 ppm within 5 min. Surprisingly, the catalyst maintain high activity even after 3 months, and the HCHO concentration decreased to.8 ppm in less than 1 min with the help of this catalyst. The catalytic performance of the monolithic catalyst showed that the La2O3 modified Pt/TiO2 catalyst possessed high activity and stability in practical application. It would be a superior catalyst in the oxidation of indoor low concentration HCHO at ambient temperature. 4. Conclusions Pt 4f BE (ev) Ti 2p BE (ev) O 1s BE (ev) 4f5/2 4f7/2 Oads Olat Oads/Olat Pt/TiO2 74.8 71.6 457.9 53.7 528.9.11 Pt/3 wt%la TiO2 74.5 71.2 457.8 53.2 529..14 HCHO concentration (ppm).6.5.4.3.2.1 Fresh 2 days 3 days 3 months. 2 4 6 8 1 12 Time on stream (min) Fig. 1. Durability test of.1% Pt/3 wt%la TiO2 monolithic catalyst for HCHO oxidation. This work demonstrated that La modified TiO2 had a dramatic promotion effect on a Pt/TiO2 catalyst for ambient HCHO oxidation. The grain size of the Pt nanoparticles was reduced to below 2 nm after the TiO2 support was modified by La2O3, which led to a higher Pt dispersion, more exposed active sites and thus superior activity for indoor low concentration HCHO oxidation. The XPS results showed that the amount of chemisorbed oxygen was more than on the unmodified support, so an enhanced metal support interaction would be another reason for its higher activity. The La modified TiO2 was wash coated on a cordierite monolith and then a very low amount of Pt (.1 wt% of the total catalyst) was supported on it. This catalyst was evaluated in a simulated indoor HCHO elimination environment, and it displayed superior purifying efficiency and stability. Therefore, it is potentially a commercial catalyst for indoor HCHO elimination References [1] J. Quiroz Torres, S. Royer, J. P. Bellat, J. M. Giraudon, J. F. Lamonier, ChemSusChem, 213, 6, 578 592. [2] Z. H. Xu, J. G. Yu, M. Jaroniec, Appl. Catal. B, 215, 163, 36 312. [3] C. B. Zhang, H. He, K. I. Tanaka, Catal. Commun., 25, 6, 211 214. [4] B. B. Chen, C. Shi, M. Crocker, Y. Wang, A. M. Zhu, Appl. Catal. B, 213, 132 133, 245 255. [5] B. Y. Bai, Q. Qiao, J. H. Li, J. M. Hao, Chin. J. Catal., 217, 38, 12 122. [6] Y. N. Shen, X. Z. Yang, Y. Z. Wang, Y. B. Zhang, H. Y. Zhu, L. Gao, M. L. Jia, Appl. Catal. B, 28, 79, 142 148. [7] X. F. Tang, Y. G. Li, X. M. Huang, Y. D. Xu, H. Q. Zhu, J. G. Wang, W. J. Shen, Appl. Catal. B, 26, 62, 265 273. [8] X. F. Tang, J. L. Chen, X. M. Huang, Y. D. Xu, W. J. Shen, Appl. Catal. B, 28, 81, 115 121. [9] C. B. Zhang, F. D. Liu, Y. P. Zhai, H. Ariga, N. Yi, Y. C. Liu, K. Asakura, M. Flytzani Stephanopoulos, H. He, Angew. Chem. Int. Ed., 212, 51, 9628 9632. [1] H. B. Huang, D. Y. C. Leung, J. Catal., 211, 28, 6 67. [11] H. B. Huang, D. Y. C. Leung, ACS Catal., 211, 1, 348 354. [12] S. Srisuda, B. Virote, J. Environ. Sci., 28, 2, 379 384. [13] T. Okachi, M. Onaka, J. Am. Chem. Soc., 24, 126, 236 237. [14] H. Nakayama, A. Hayashi, T. Eguchi, N. Nakamura, M. Tsuhako, Solid State Sci., 22, 4, 167 17. [15] C. H. Ao, S. C. Lee, J. Z. Yu, J. H. Xu, Appl. Catal. B, 24, 54, 41 5. [16] B. Ohtani, Chem. Lett., 28, 37, 217 229. [17] J. H. Mo, Y. P. Zhang, Q. J. Xu, J. J. Lamson, R. Y. Zhao, Atmos. Environ., 29, 43, 2229 2246. [18] S. Sun, J. J. Ding, J. Bao, C. Gao, Z. M. Qi, C. X. Li, Catal. Lett., 21, 137, 239 246. [19] D. W. Kwon, P. W. Seo, G. J. Kim, S. C. Hong, Appl. Catal. B, 215,

46 Honggen Peng et al. / Chinese Journal of Catalysis 38 (217) 39 47 Chin. J. Catal., 217, 38: 39 47 Graphical Abstract doi: 1.116/S1872 267(16)62532 9 La doped Pt/TiO2 as an efficient catalyst for room temperature oxidation of low concentration HCHO Honggen Peng *, Jiawei Ying, Jingyan Zhang, Xianhua Zhang, Cheng Peng, Cheng Rao, Wenming Liu, Ning Zhang, Xiang Wang * Nanchang University; Shanghai Jiao Tong University La doped TiO2 was used to support Pt and the catalyst displayed superior catalytic performance in the removal of low concentration HCHO at room temperature. 163, 436 443. [2] L. Zeng, W. L. Song, M. H. Li, D. W. Zeng, C. S. Xie, Appl. Catal. B, 214, 147, 49 498. [21] J. Quiroz, J. M. Giraudon, A. Gervasini, C. Dujardin, C. Lancelot, M. Trentesaux, J. F. Lamonier, ACS Catal., 215, 5, 226 2269. [22] N. H. An, Q. S. Yu, G. Liu, S. Y. Li, M. J. Jia, W. X. Zhang, J. Hazard. Mater., 211, 186, 1392 1397. [23] B. Y. Bai, Q. Qiao, J. H. Li, J. M. Hao, Chin. J. Catal., 217, 38, 27 31. [24] H. Y. Chen, M. N. Tang, Z. B. Rui, H. B. Ji, Ind. Eng. Chem. Res., 215, 54, 89 897. [25] C. Y. Ma, D. H. Wang, W. J. Xue, B. J. Dou, H. L. Wang, Z. D. Hao, Environ. Sci. Technol., 211, 45, 3628 3634. [26] B. Y. Bai, H. Arandiyan, J. H. Li, Appl. Catal. B, 213, 142 143, 677 683. [27] H. Y. Chen, Z. B. Rui, H. B. Ji, Chin. J. Catal., 215, 36, 188 196. [28] L. H. Nie, A. Y. Meng, J. G. Yu, M. Jaroniec, Sci. Rep., 213, 3, 3215. [29] H. B. Huang, X. G. Ye, H. L. Huang, L. Zhang, D. Y. C. Leung, Chem. Eng. J., 213, 23, 73 79. [3] X. Wang, R. J. Gorte, J. P. Wagner, J. Catal., 22, 212, 225 23. [31] W. J. Shen, A. Kobayashi, Y. Ichihashi, Y. Matsumura, M. Haruta, Catal. Lett., 21, 73, 161 165. [32] M. S. Jin, H. Y. Liu, H. Zhang, Z. X. Xie, J. Y. Liu, Y. N. Xia, Nano Res., 21, 4, 83 91. [33] X. Wang, D. P. Liu, J. Q. Li, J. M. Zhen, F. Wang, H. J. Zhang, Chem. Sci., 215, 215, 2877 2884. [34] J. S. Tian, H. G. Peng, X. L. Xu, W. M. Liu, Y. H. Ma, X. Wang, X. J. Yang, Catal. Sci. Technol., 215, 5, 227 2281. [35] X. L. Xu, X. Wang, Y. C. Li, J. S. Tian, W. M. Liu, Z. X. Gao, Z. Phys. Chem., 214, 228, 27 48. [36] X. Wang, J. S. Tian, Y. H. Zheng, X. L. Xu, W. M. Liu, X. Z. Fang, ChemCatChem, 214, 6, 164 1611. [37] H. G. Peng, Y. H. Ma, W. M. Liu, X. L. Xu, X. Z. Fang, J. Lian, X. Wang, C. Q. Li, W. F. Zhou, P. Yuan, J. Energy Chem., 215, 24, 416 424. [38] Y. H. Ma, X. Wang, X. J. You, J. J. Liu, J. S. Tian, X. L. Xu, H. G. Peng, W. M. Liu, C. Q. Li, W. F. Zhou, P. Yuan, X. H. Chen, ChemCatChem, 214, 6, 3366 3376. [39] J. J. Liu, H. G. Peng, W. M. Liu, X. L. Xu, X. Wang, C. Q. Li, W. F. Zhou, P. Yuan, X. H. Chen, W. G. Zhang, H. B. Zhan, ChemCatChem, 214, 6, 295 214. [4] L. Zhang, L. Wang, Z. Y. Jiang, Z. X. Xie, Nanoscale Res. Lett., 212, 7, 312 318. [41] T. T. Zhang, H. Y. Zhao, S. N. He, K. Liu, H. Y. Liu, Y. D. Yin, C. B. Gao, ACS Nano, 214, 8, 7297 734. [42] H. X. Hei, H. He, R. Wang, X. J. Liu, G. Z. Zhang, Soft Nanosci. Lett., 212, 2, 34 4. [43] Y. S. She, Q. Zheng, L. Li, Y. Y. Zhan, C. Q. Chen, Y. H. Zheng, X. Y. Lin, Int. J. Hydrogen Energy, 29, 34, 8929 8936. [44] J. R. Gaudet, A. De La Riva, E. J. Peterson, T. Bolin, A. K. Datye, ACS Catal., 213, 3, 846 855. [45] F. Wang, G. X. Lu, J. Power Sources, 28, 181, 12 126. [46] D. Gonzalez, E. Lima, N. Martín, Ind. Eng. Chem. Res., 27, 46, 4335 434. [47] C. Anjaneyulu, G. Naresh, V. V. Kumar, J. Tardio, T. V. Rao, A. Venugopal, ACS Sustain. Chem. Eng., 215, 3, 1298 135. [48] S. Colussi, C. de Leitenburg, G. Dolcetti, A. Trovarelli, J. Alloys Compd., 24, 374, 387 392. La 掺杂 TiO 2 负载 Pt 催化剂制备及其室温氧化低浓度甲醛 彭洪根 a,b,*,, 应家伟 a,, 张景岩 a, 张先华 a, 彭程 a, 饶成 a, 刘文明 a, 张宁 a, 王翔 a,# a 南昌大学化学学院, 应用化学研究所, 江西南昌 3331 b 上海交通大学化学化工学院, 上海 224 摘要 : 甲醛是室内装修污染的重要组分, 已严重危害到人们身体健康, 在室温条件下消除甲醛引起了人们的广泛兴趣. 目前室温清除甲醛主要有物理吸附法 光催化法 等离子体技术及催化氧化技术. 物理吸附法主要采用活性炭等作为吸附剂, 其初期吸附效果较好, 但当吸附饱和之后会重新释放甲醛造成二次污染 ; 光催化法和等离子体技术需要特殊装置, 不适合室内室温环境脱除甲醛 ; 而催化氧化技术则可直接将甲醛转化为无毒无害的水和 CO 2, 因而备受关注. Pt/TiO 2 被认为是目前消除甲醛最有效的催化剂. 为进一步降低贵金属 Pt 的用量及增强其稳定性 (Pt 被氧化后其活性会降低 ), 本文首次

Honggen Peng et al. / Chinese Journal of Catalysis 38 (217) 39 47 47 采用稀土 La 掺杂锐钛矿型 TiO 2, 负载少量 Pt 后用于室内低浓度 (.5 ppm) 甲醛的催化氧化. 活性测试结果表明, 纯 TiO 2 催化剂上甲醛转化率在 5% 以下, 有可能是物理吸附或可见光催化所致. 负载.5% Pt 后, Pt/TiO 2 和 Pt/La-TiO 2 甲醛转化率均高于 8%, 尤其是 La 掺杂活性高达 96% 以上, 且在连续反应 8 h 甚至延长至 4 h 后其活性均未见下降趋势. 电镜结果表明, La 掺杂 Pt/La-TiO 2 催化剂中 Pt 粒径从未掺杂的 2.2 nm 降至 1.7 nm; CO 程序升温脱附测试表明, Pt/La-TiO 2 /Pt 的分散度达 66%, 而未掺杂样品仅为 51%; X 射线光电子能谱测试表明, Pt/La-TiO 2 的表面氧物种高于 Pt/TiO 2 催化剂, 说明 La 掺杂增强了 Pt 和载体间的相互作用. 为探讨 Pt/La-TiO 2 商业化应用前景, 将粉体 Pt/La-TiO 2 涂覆在堇青石蜂窝陶瓷上制备成整体催化剂. 该整体催化剂在容积为 2 m 3 的密室测试中 5 min 内即可将浓度为.5 ppm 的甲醛将至.2 ppm 以下. 该催化剂在存放 3 个月后活性略有下降, 但在 1 min 内仍可将甲醛浓度降至.8 ppm, 达到室内甲醛排放标准. 综上, 本文成功制备了 La 掺杂 Pt/La-TiO 2 用于室内低浓度甲醛催化氧化, 该催化剂表现出优异的催化性能. 通过多种表征手段表明, La 修饰后贵金属 Pt 纳米粒子尺寸减小 分散度提高及 Pt 与载体间相互作用增强是其活性优异的主要原因. 以 Pt/La-TiO 2 粉体制备的整体催化剂同样表现出了高的催化性能, 具有工业应用前景. 关键词 : 低浓度甲醛 ; 室温氧化 ; 稀土 ; 镧掺杂 ; 铂 ; 二氧化钛 ; 整体催化剂 收稿日期 : 216-8-3. 接受日期 : 216-9-21. 出版日期 : 217-1-5. * 通讯联系人. 电话 : 158351832; 电子信箱 : penghonggen@ncu.edu.cn # 通讯联系人. 电话 : 15979149877; 电子信箱 : xwang23@ncu.edu.cn 这些作者对本文工作贡献相同. 基金来源 : 国家重点研发计划 (216YFC259); 国家自然科学基金 (215316, 2156716); 江西省科技落地计划 (KJLD145); 江西省自然科学基金 (2142BAB21313, 2151BBE56). 本文的英文电子版由 Elsevier 出版社在 ScienceDirect 上出版 (http://www.sciencedirect.com/science/journal/1872267).